Does Converting JPG to PNG Improve Quality? (Honest Answer)
A very common belief is that saving a JPG as PNG will make it higher quality. It will not, and it is worth understanding why.
The short answer: no
A JPG has already lost information during its lossy compression. Converting it to PNG stores the pixels it currently has without any further loss, but it cannot bring back what was discarded. The result looks identical to the JPG, usually at several times the file size.
Why the PNG is so much bigger
JPG is designed to shrink photos by dropping detail. PNG is designed to keep every pixel exactly. A 500 KB photo can become a 3 to 6 MB PNG because lossless compression finds little to squeeze in photographic noise.
When converting to PNG is a good idea
Some programs and forms only accept PNG. If you plan to edit the picture many times, saving it as PNG during the work avoids stacking more JPG compression. You may also want PNG when adding transparency later in an editor, since JPG cannot hold it.
It will not create transparency
Converting a JPG with a white background to PNG leaves the white background as it is. The new file supports transparency, but nothing in it is transparent. Removing the background needs an editor or a background remover.
How to get better quality instead
Go back to the original source. Re-export from the RAW file, design file or camera original at a higher quality, or use a larger version of the image. If you only have the small JPG, a tidy resize and a light sharpen are as good as it gets.